The present invention relates to semiconductor manufacturing equipment, and more particularly to a method for reducing particle concentration within a semiconductor device fabrication tool.
In the semiconductor device fabrication industry a single defect can destroy an entire wafer die by shorting a junction region or open-circuiting a gate electrode of an essential semiconductor device. Defects also degrade device performance and reliability by creating leakage paths, generating undesirable localized fields, and the like.
A defect can arise when a particle lands on a wafer. Particles commonly arise from humans, the environment in which the wafer is processed (e.g., particles generated by friction between moving objects within the processing chamber), as well as from films deposited or grown on the wafer.
To reduce particle-induced defects, wafers are fabricated in a vacuum environment within a sealed semiconductor device fabrication tool (hereinafter xe2x80x9cfabrication toolxe2x80x9d). A fabrication tool typically includes at least one load lock that receives a wafer carrier containing one or more wafers, and that places the wafer carrier in a vacuum environment; at least one vacuum processing chamber for performing processing on wafers extracted from the wafer carrier, and at least one transfer chamber containing a wafer handler adapted to transfer wafers between the load lock and the processing chamber. Conventionally these fabrication tools are housed within an enclosed area known as a clean room, having filters and/or other mechanisms for removing particles from the environment.
A clean room is monitored to ensure that the level of particles per cubic foot of clean room does not exceed a predetermined level or clean room xe2x80x9cclassxe2x80x9d. However, due to the amount of filtering required and the cost of acquiring, maintaining and operating the filtering equipment, it is extremely expensive to achieve the highly clean environment required of an area in which a wafer or wafer carrier is exposed to the environment outside the fabrication tool. Typically a class 1 environment containing fewer than about 1 particle of 0.5 micron size or larger per cubic foot of air is required of such areas. Accordingly, because a fabrication tool maintains wafers and wafer carriers in a vacuum environment after they are loaded into the load lock and pumped down to vacuum pressure, the clean room surrounding the fabrication tool typically is divided into two areas, a white area having a high cleanliness level and a gray area having a lower cleanliness level than the white area. Wafers and/or wafer carriers are typically only exposed to a fabrication tool""s external environment when the wafers and/or wafer carriers are adjacent the load lock. Accordingly only the area adjacent the load lock is maintained at the high cleanliness level (e.g., a class 1 cleanliness level) referred to as a white area (or white environment). The remainder of the fabrication tool is kept within the less clean or lower clean room class area referred to as a gray area (or gray environment), typically having a class 100 environment having fewer than about 10 particles of 0.5 micron size or larger per cubic foot of air.
To keep the interior of the fabrication tool itself clean, a vacuum atmosphere is maintained within the fabrication tool as continuously as possible, and extensive measures are taken to reduce moving parts and other sources of particle generation within the fabrication tool. Despite these measures, and despite maintenance of a clean room environment external to the fabrication tool, the occurrence of defect generating particles within fabrication tools remains perplexingly problematic. Accordingly, there is a need for a method which further reduces particle concentration within a semiconductor device fabrication tool.
The present inventors have discovered that a significant number of potentially defect generating particles which exist within a fabrication tool are neither generated within the tool, nor enter through the load locks. Rather, it has been discovered that these particles enter the fabrication tool when a given chamber is opened for maintenance (i.e., repair or routine maintenance). During maintenance a chamber is opened and the chamber""s interior is conventionally exposed to the gray area environment which surrounds the fabrication tool. Although typically no wafer is exposed to the gray area environment, particles enter the chamber from the gray area and subsequently are not able to be completely removed from the interior of the chamber by the chamber""s vacuum pump.
To overcome the shortcomings of the prior art, the present inventors provide a method for reducing the number of particles within a chamber of a fabrication tool that is located within a gray area of a clean room and, absent the inventive method, would be exposed to a gray area environment when opened. The invention provides a portable clean room station that is configured so as to provide a white environment (or any environment cleaner than the environment in which the fabrication tool is located). The portable clean room station surrounds at least the open portion of a fabrication tool""s open chamber.
Preferably the environment provided by the portable clean room station is selected so as to have at least two orders of magnitude fewer particles per cubic foot of air than the gray area environment in which the portable clean room station is located.
By providing a portable clean room station within the gray area which surrounds a fabrication tool, a chamber of a fabrication tool may be exposed to significantly fewer potential defect generating particles when opened (e.g., during preventative maintenance, repair or other chamber maintenance), despite being physically located within the gray area. Device quality and chamber cleanliness thereby are significantly enhanced, and the cost of surrounding the entire fabrication tool with a white area environment is avoided.
Other objects, features and advantages of the present invention will become more fully apparent from the following detailed description of the preferred embodiments, the appended claims and the accompanying drawings.